This invention relates to the retorting of oil shale. More specifically, this invention relates to an improved process and apparatus for the retorting of oil shale, the production of spent oil shale having improved cementation properties, and the recovery of energy from the process.
The term "oil shale" refers to sedimentary deposits containing organic materials which can be converted to shale oil. Oil shale can be found in various places throughout the world, especially in the United States in Colorado, Utah, and Wyoming. Some especially important deposits can be found in the Green River formation in the Piceance Basin, Garfield and Rio Blanco counties, in Northwestern Colorado.
Oil shale contains organic material called kerogen which is a solid carbonaceous material from which shale oil can be produced. Commonly oil shale deposits have variable richness of kerogen content, the oil shale generally being stratified in horizontal layers. Upon heating oil shale to a sufficient temperature, kerogen is decomposed and liquids and gases are formed. These fluids contain heating values and comprise shale oil, carbon monoxide, carbon dioxide, hydrogen, light hydrocarbon gases, water, hydrogen sulfide, and others. Oil shale can be retorted to form a hydrocarbon liquid either by in situ or surface retorting. In surface retorting, oil shale is mined from the ground, brought to the surface, crushed, and placed in vessels where it is contacted with hot heat transfer medium, such as hot shale or gases, or mixtures thereof, for heat transfer. The resulting high temperatures cause shale oil to be freed from the oil shale forming a partially spent oil shale comprising inorganic material and carbonaceous material such as coke. The coke may be deposited on the surface of the shale particles and also within the shale particles The carbonaceous material can be burned by contact with oxygen at oxidation temperatures to recover heat and to form a spent oil shale relatively free of carbon. Spent retorted oil shale which has been depleted in carbonaceous material is removed from the reactor and discarded. Some well-known methods of surface retorting are the Tosco, Lurgi, and Paraho processes and fluid bed retorting, among others.
In the Lurgi type retort, raw fresh shale is fed into a mixer wherein it is contacted with hot spent or partially spent shale. The combined oil shales are then fed into a zone for additional residence time. Shale oil which has been retorted from the oil shale is separated from the shale. The oil is recovered and the spent and partially spent shale is passed to a zone wherein carbon is burned off the shale. This can be done by introducing oxygen containing gas such as air or diluted oxygen, and sometimes additional fuel to the zone to combust the carbon. A preferred method is to pass the spent and partially spent shale, and air or air and fuel upwardly through a vertical elongated zone such as a lift pipe. After oxidation, a portion of the spent shale is then removed from the flue gas from said zone, for example by electrostatic precipitators, and used for the manufacture of solid masses. Another portion of the spent shale is fed to the mixer to transfer heat to fresh oil shale. This process is more fully described in U.S. Pat. No. 3,655,518 which is incorporated by reference and made a part hereof.
In fluid bed retorting, crushed shale is contacted with hot spent shale and/or hot gases in a fluid bed. The fluid bed may be an elongated vertical zone wherein solids are introduced at or near the bottom and maintained in a fluidized state by high gas velocity. However, fluid bed retort may have many configurations. High temperatures cause oil shale and partially spent oil shale to be formed. Solids are separated from liquid and gaseous products, and partially spent oil shale containing carbonaceous material is passed to a fluidized oxidation zone to burn the carbonaceous material and form spent oil shale relatively free of carbon for recycle or for disposal. Mitchell et al., U.S. Pat. Nos. 4,183,800 and 4,133,739; Tamm et al., U.S. Pat. No. 4,125,453 and Langlois et al., U.S. Pat. No. 4,087,347 are just a few patents which describe fluid bed retorting and are incorporated by reference and made a part hereof.
Knepper et al., U.S. Pat. No. 4,120,355 and Watson et al., U.S. Pat. No. 4,131,416, teach the introduction of aqueous slurries of spent oil shale from surface retorting into spent subterranean in situ oil shale retorts to form mechanically strong structures. These structures can prevent surface subsidence above the retort, and prevent leaching of chemicals from the mass of rubblized spent shale underground.
O'Neal, U.S. Pat. No. 3,459,003 teaches the use of slurries of spent shale from surface retorting and water, and in some cases cement, for forming of a competent mass having structural strength underground.
Fondriest, U.S. Ser. No. 803,730, filed June 6, 1977, teaches the use of concrete, sometimes containing spent oil shale from surface retorting, to fill underground voids formed from the mining of oil shale or coal. The concrete forms load bearing pillars so that support pillars of hydrocarbonaceous material can be removed.
In order for a slurry of water and spent oil shale from surface retorting to be suitable to form a mechanically strong and environmentally acceptable structure, the spent oil shale preferably has certain properties. The spent shale should contain less than about 0.5 weight percent carbon, still more preferably less than about 0.2 weight percent carbon, so that the spent shale can be suitably wetted by water. Preferably at least about 90 weight percent of the spent shale should be smaller than about 150 mesh, more preferably smaller than about 200 mesh. Also, the spent shale desirably contains a reasonable content of inorganic oxides. This can be accomplished by converting carbonates in the partially spent shale to oxides by thermal decomposition.
In order to assure good heat contact between fresh oil shale feed and spent shale recycle, and good grinding action due to recirculation in the retort contacting zone resulting in fine particle size of partially spent and spent shale, high recycle rates of spent shale to feed shale are desirable.
It is an object of this invention to provide an improved method and apparatus for the retorting of oil shale while producing a fine spent shale with improved concentration properties due primarily to its fineness.
It is an object of this invention to provide a method and apparatus for manufacturing spent oil shale from surface retorting which has improved cementation properties and is suitable for disposal.
It is an object of this invention to provide a retorting process which enhances the conversion of inorganic carbonates to oxides and eliminates the need for a separate calcination step for the manufacture of improved spent shale.